February 26, 2025, Planning Board Special Meeting Transcript - WEHI

03/03/2025 06:36:47 AM Page 21 to 24 of 115 6 of 46 sheets 21 So you're probably asking yourself, how do you do1 that. What you do is you go to the modeling. We look2 at their model, we decide -- they show how much water3 they're going to infiltrate during the 100-year storm.4 So let me go to the model for one moment.5 At this point the model as in M-O-D-E-L?6 Q. Yeah, the stormwater model, M-O-D-E-L.7 A. Okay. Right now we're looking at the stormwater8 report provided by the applicant. This is for basin9 number 3, that's what they call porous pavement section10 number 3. It's essentially an underground stormwater11 basin. You'll see here, this is kind of a -- they use12 the modeling software HydroCAD, which is a summary of13 different volumes. Discarded section is the14 infiltration. It's discarded because it doesn't go into15 any of the pipes. It just kind of goes away. It16 disappears. Right. So they say that during the17 100-year storm, which is shown right here, they're going18 to infiltrate 10,971 cubic feet of water. So now, we19 have to translate that into a height, we're looking at a20 profile and right then on the same page they give the21 surface area of the basin, which is 5,227. So if you22 divide the 10,000 number by the 2 -- by the 5,00023 number, you roughly get two feet of water. So that24 means you're going to have two feet of standing water in25 22 that basin that they got to hold before the storage.1 Let me go back to the plan.2 Now, I'm going to go back to the plan. So now3 what you're thinking is, all right, so tell me, talk4 about how long. Right. Here it says two feet, no5 problem. That's two feet full of sand. We're talking6 about two feet vertical of just plain vertical water.7 So you have to fit the water with the sand. Sand8 significantly has what we call a void ratio of 0.4.9 Which means if you have one cubic foot of sand, 4010 percent of it is empty space. So you would take that11 two feet of water and you would divide it by 0.4, and12 that's how high -- that's the height you would have of13 water with sand.14 All right. When you divide two -- it's 2.1, when15 you divide 2.1 by 0.4 you have 5.25 feet of water. And16 at this point it's going to exceed the height of17 pavement. Again, the water's being held, the water's18 going to be trapped by this slow infiltrate soil, it's19 going to build up in the sand, it's going to exceed

it's going to exceed the height of17 pavement. Again, the water's being held, the water's18 going to be trapped by this slow infiltrate soil, it's19 going to build up in the sand, it's going to exceed the20 sand depth, it's going to fill up the void space in the21 storage area, more water's going to go through the pipe.22 The amount of peak flow rates they show in the models23 aren't correct. It's going to capture, the storage is24 going to -- sorry, the runoff is going to go more25 23 through the pipes and it's going to run into this wall.1 What happens it when goes through the pipes?2 Q. When it goes through the pipes the peak flow rate3 A. they report in the model is inaccurate, it's under.4 It's going to be higher, which means that they have5 limitations on how high they can make the peak flow6 runoff for this developed site. It's supposed to be7 less than what exists and right now for this situation8 it's going to be higher for the larger storms.9 Now, we saw -- now, I used porous pavement10 section number 3, we saw the same instance in porous11 pavement number 4, 5, 6, basin 7, 8, 9 and basin 10. So12 now, I'm not going to through all these because I13 respect your time, but I want to detail an example. It14 wasn't always this extreme but in those basins the15 stormwater, it's going to affect the peak flow runoff16 rate, which is really crucial because we do have17 flooding downstream and we have to meet certain peak18 flow rate reductions and what they are reporting is not19 going to happen in reality. These basins are going to20 be strained by the storage from too much flow, too much21 runoff being trapped and we're going to have higher peak22 flow rates.23 What does that translate to in terms of practical24 Q. counts?25 24 It means that the water's not going to infiltrate1 A. like the model says. It means more water in the pipes,2 more water going downstream and you can potentially3 increase the water coming off the site and reduce it,4 which you're supposed be doing according to the5 standards and if you increase the runoff you can get6 flooding, or you can get more flooding.7 All right. I would like to, now that we propose8 a new high water table, I would like to take a moment to9 talk about runoff in general.10 Let me just identify the screen, if I can.11 Q. CHAIRMAN BAGOFF: One second, I'm sorry.12 Let it be noted Mr. Cardoza joined the planning

ould like to take a moment to9 talk about runoff in general.10 Let me just identify the screen, if I can.11 Q. CHAIRMAN BAGOFF: One second, I'm sorry.12 Let it be noted Mr. Cardoza joined the planning board.13 Thank you.14 MR. AFRAN: It says on the bottom, Figure 1,15 Proposed Grading Plan. And then it has additional16 words, With blue arrows showing the existing drainage17 path and the red arrows showing the proposed drainage18 path and how the runoff is being diverted from the19 wetlands. I'm just reciting that so we have a reference20 point.21 This figure is from the letter we submitted to22 A. the DEP based on our review of the applicants23 submission.24 MS. MCGOVERN: O-5, that we marked November25